Long-Term Debt and Commitments Related to Letters of Credit (Narrative) (Details)	3 Months Ended
	Mar. 30, 2019 USD ($)	Feb. 05, 2019 USD ($)	Dec. 31, 2018 USD ($)	May 07, 2017 USD ($)
Debt Instrument [Line Items]
Revolving credit facility, current borrowing capacity	$ 250,000,000
Revolving credit facility, maximum borrowing capacity	325,000,000
Unused commitments under credit facility	157,377,000
Revolving credit facility borrowings	$ 89,500,000		$ 93,500,000
Number of principal payments	5	5
Long-term debt, maturities, repayments of principal in next twelve months	$ 16,151,000
Long-term debt, maturities, repayments of principal in year two	7,917,000
Long-term debt, maturities, repayments of principal in year three	5,440,000
Long-term debt, maturities, repayments of principal in year four	89,700,000
Long-term debt, maturities, repayments of principal in year five	0
Long-term debt, maturities, repayments of principal after year five	$ 75,000,000
Anniversary when principal payments begin	6
Minimum [Member]
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.10%
Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.225%
Swing-line borrowings [Member]
Debt Instrument [Line Items]
Revolving credit facility, current borrowing capacity	$ 25,000,000
Revolving credit facility borrowings	$ 8,500,000		$ 2,500,000
Revolving credit facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest coverage ratio	3
Revolving credit facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital	3
5.09% Senior unsecured notes [Member]
Debt Instrument [Line Items]
Interest rate	5.09%
Debt Instrument, Face Amount	$ 30,000,000
3.99% Senior unsecured notes [Member]
Debt Instrument [Line Items]
Interest rate	3.99%
Unsecured debt maximum borrowing capacity allowed by credit facility	$ 75,000,000
Unsecured debt additional shelf note capacity	50,000,000
Debt Instrument, Face Amount	$ 50,000,000
Unsecured debt additional shelf note capacity allowed by credit facility		$ 25,000,000
4.00% Senior unsecured notes [Member]
Debt Instrument [Line Items]
Interest rate		4.00%
Unsecured debt additional shelf note capacity		$ 25,000,000
Accounts receivable securitization [Member]
Debt Instrument [Line Items]
Interest rate	0.90%
Unused commitment fee threshold percent	0.50
Debt instrument variable rate base rate calculation, default rate	2.00%
Accounts receivable securitization [Member] | Base Rate, Federal Funds [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.50%
Line of credit [Member]
Debt Instrument [Line Items]
Revolving credit facility borrowings	$ 92,623,000
Line of credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	1.50%
Line of credit [Member] | Base Rate, Federal Funds [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.50%
Line of credit [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.875%
Line of credit [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	1.50%
Letter of credit [Member]
Debt Instrument [Line Items]
Letters of credit issued	$ 72,565,000
Letter of credit [Member] | Revolving credit facility [Member]
Debt Instrument [Line Items]
Letters of credit issued	3,123,000
Letter of credit [Member] | Accounts receivable securitization [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity				$ 100,000,000
Letters of credit issued	$ 67,438,000
Debt instrument, term	1 year
Letter of credit [Member] | Accounts receivable securitization [Member] | Minimum [Member]
Debt Instrument [Line Items]
Letter of credit, unused capacity, commitment fee percentage	0.0035
Letter of credit [Member] | Accounts receivable securitization [Member] | Maximum [Member]
Debt Instrument [Line Items]
Letter of credit, unused capacity, commitment fee percentage	0.0045
Letter of credit [Member] | Line of credit [Member]
Debt Instrument [Line Items]
Letters of credit issued	$ 2,004,000
Letter of credit [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 100,000,000